Combustion of a single emulsion fuel droplet in a rapid compression machine

• Combustion of a fuel emulsion droplet was studied in a rapid compression machine.
• Ignition delay and combustion stage by experimental conditions were observed.
• The effect of the droplet temperature and the micro-explosion was discussed.

The autoignition and combustion characteristics of a single water/n-decane emulsion droplet were examined using a rapid compression machine. A specific volume ratio of water was added to the n-decane, and a water-in-oil emulsion was formed by ultrasonication. The emulsion droplet was suspended at the tip of a fine thermocouple and placed at the center of the reaction chamber. The time evolutions of droplet temperature and diameter were observed. Droplet combustion was classified into four stages, and the characteristics of each stage varied little with the water volume ratio. Ignition delay increased monotonically with initial droplet diameter and water volume ratio. Increasing the water ratio boosted the intensity of micro explosions, while the rise in droplet temperature was hindered by the specific heat and latent heat of the water. The average burning rate was elevated when the initial droplet diameter increased. However, the burning rate was not affected much by the water volume ratio.